Control of infinitely variable transmission

Abstract

A controller calculates a target speed ratio of a continuously variable transmission incorporated into an infinitely variable transmission for a vehicle and a target vehicle speed according to a vehicle running state. When a predetermined creep torque limiting condition holds, the controller limits the target vehicle speed such that the difference between the target vehicle speed and the real vehicle speed is within a predetermined range. By controlling the speed ratio of the continuously variable transmission such that this difference diminishes, the infinitely variable transmission generates a creep torque consistent with the intention of the driver.

What is claimed is:  
     
       1. A control device for an infinitely variable transmission for a vehicle, the infinitely variable transmission comprising an input shaft, a continuously variable transmission which outputs the rotation of the input shaft at an arbitrary speed ratio, a fixed speed ratio transmission which outputs the rotation of the input shaft at a fixed speed ratio, and an output shaft which changes a rotation direction and a rotation speed according to a difference between an output rotation speed of the continuously variable transmission and an output rotation speed of the fixed speed ratio transmission, the device comprising: 
       a sensor which detects a running state of the vehicle;  
       a sensor which detects a real vehicle speed; and  
       a programmable controller programmed to:  
       calculate a target speed ratio of the continuously variable transmission based on the running state of the vehicle;  
       set a target vehicle speed based on the running state of the vehicle;  
       determine if a predetermined creep torque control condition holds based on the running state of the vehicle;  
       limit the target vehicle speed, if the predetermined condition holds, to cause a difference between the target vehicle speed and the real vehicle speed to be within a predetermined range;  
       calculate a corrected target speed ratio by correcting the target speed ratio to cause a difference between a limited target vehicle speed and the real vehicle speed to become smaller; and  
       control the speed ratio of the continuously variable transmission based on the corrected target speed ratio.  
     
     
       2. The control device as defined in  claim 1 , wherein, the controller is further programmed to set a transient target speed ratio of the infinitely variable transmission based on the running state, calculate a transient target speed ratio of the continuously variable transmission from the transient target speed ratio of the infinitely variable transmission, calculate a feedback correction amount based on the difference between the limited target vehicle speed and the real vehicle speed, and calculate the corrected target speed ratio by adding the feedback correction amount to the transient target speed ratio of the continuously variable transmission. 
     
     
       3. The control device as defined in  claim 1 , wherein, the vehicle running state detecting sensor comprises a sensor which detects a depression state of an accelerator pedal with which the vehicle is provided, and the controller is further programmed to determine that the predetermined condition does not hold when the accelerator pedal is depressed. 
     
     
       4. The control device as defined in  claim 1 , wherein, the controller is further programmed to determine that the predetermined condition does not hold when the real vehicle speed is greater than a predetermined first vehicle speed. 
     
     
       5. The control device as defined in  claim 1 , wherein, the vehicle running state detecting sensor comprises a sensor which detects an operation state of a brake with which the vehicle is provided, and the controller is further programmed set the predetermined range according to the operation state of the brake. 
     
     
       6. The control device as defined in  claim 5 , wherein, the controller is further programmed to limit the target vehicle speed, when the brake does not operate, by an upper limit determined according to the real vehicle speed, and limit the target vehicle speed, when the brake operates, by a lower limit determined according to the real vehicle speed. 
     
     
       7. The control device as defined in  claim 1 , wherein, the vehicle running state detecting sensor comprises a sensor which detects a depression amount of an accelerator pedal with which the vehicle is provided, and the controller is further programmed to set a target output torque of the output shaft based on the depression amount of the accelerator pedal, calculate a target vehicle acceleration based on the target output torque of the output shaft, and set the target vehicle speed before limitation to be equal to an integral of the target vehicle acceleration. 
     
     
       8. The control device as defined in  claim 7 , wherein the vehicle running state detecting sensor comprises a sensor which detects an operation state of a brake with which the vehicle is provided, and the controller is further programmed to set the target output torque to a smaller value when the brake operates than when the brake does not operate. 
     
     
       9. The control device as defined in  claim 7 , wherein the controller is further programmed to calculate a torque shift compensation amount based on the target output torque, and control the speed ratio of the continuously variable transmission based on a sum of the corrected target speed ratio and the torque shift compensation amount. 
     
     
       10. The control device as defined in  claim 1 , wherein the vehicle running state detecting sensor comprises a sensor which detects a stationary state of the vehicle, and the controller is further programmed to control the speed ratio of the continuously variable transmission when the vehicle is in the stationary state to cause the rotation speed of the output shaft to become zero. 
     
     
       11. A control device for an infinitely variable transmission for a vehicle, the infinitely variable transmission comprising an input shaft, a continuously variable transmission which outputs the rotation of the input shaft at an arbitrary speed ratio, a fixed speed ratio transmission which outputs the rotation of the input shaft at a fixed speed ratio, and an output shaft which changes a rotation direction and a rotation speed according to a difference between an output rotation speed of the continuously variable transmission and an output rotation speed of the fixed speed ratio transmission, the device comprising: 
       means for detecting a running state of the vehicle;  
       means for detecting a real vehicle speed;  
       means for calculating a target speed ratio of the continuously variable transmission based on the running state of the vehicle;  
       means for setting a target vehicle speed based on the running state of the vehicle;  
       means for determining if a predetermined creep torque control condition holds based on the running state of the vehicle;  
       means for limiting the target vehicle speed, if the predetermined condition holds, to cause a difference between the target vehicle speed and the real vehicle speed to be within a predetermined range;  
       means for calculating a corrected target speed ratio by correcting the target speed ratio to cause a difference between a limited target vehicle speed and the real vehicle speed to become smaller; and  
       means for controlling the speed ratio of the continuously variable transmission based on the corrected target speed ratio.  
     
     
       12. A control method for an infinitely variable transmission for a vehicle, the infinitely variable transmission comprising an input shaft, a continuously variable transmission which outputs the rotation of the input shaft at an arbitrary speed ratio, a fixed speed ratio transmission which outputs the rotation of the input shaft at a fixed speed ratio, and an output shaft which changes a rotation direction and a rotation speed according to a difference between an output rotation speed of the continuously variable transmission and an output rotation speed of the fixed speed ratio transmission, the method comprising: 
       detecting a running state of the vehicle;  
       detecting a real vehicle speed;  
       calculating a target speed ratio of the continuously variable transmission based on the running state of the vehicle;  
       setting a target vehicle speed based on the running state of the vehicle;  
       determining if a predetermined creep torque control condition holds based on the running state of the vehicle;  
       limiting the target vehicle speed, if the predetermined condition holds, to cause a difference between the target vehicle speed and the real vehicle speed to be within a predetermined range;  
       calculating a corrected target speed ratio by correcting the target speed ratio to cause a difference between a limited target vehicle speed and the real vehicle speed to become smaller; and  
       controlling the speed ratio of the continuously variable transmission based on the corrected target speed ratio.  
     
     
       13. A control device for an infinitely variable transmission for a vehicle, the infinitely variable transmission comprising an input shaft, a continuously variable transmission which outputs the rotation of the input shaft at an arbitrary speed ratio, a fixed speed ratio transmission which outputs the rotation of the input shaft at a fixed speed ratio, and an output shaft which changes a rotation direction and a rotation speed according to a difference between an output rotation speed of the continuously variable transmission and an output rotation speed of the fixed speed ratio transmission, the device comprising: 
       a sensor which detects a running state of the vehicle;  
       a sensor which detects a real vehicle speed; and  
       a programmable controller programmed to:  
       calculate a target speed ratio of the continuously variable transmission based on the running state of the vehicle;  
       set a target vehicle speed based on the running state of the vehicle;  
       determine if a predetermined creep torque control condition holds based on the running state of the vehicle;  
       calculate, if the predetermined condition holds, a corrected target speed ratio by correcting the target speed ratio to cause a ratio of a rotation speed of the input shaft and a rotation speed of the output shaft to become smaller as the target vehicle speed becomes greater; and  
       control the speed ratio of the continuously variable transmission based on the corrected target speed ratio.